SNS and HFIR provide exceptional neutron source materials characterization capabilities.
ORNL's neutron sciences program is in the enviable position of having a user program that combines access to the Spallation Neutron Source (SNS), the world's most powerful pulsed neutron source, with entrée to the High Flux Isotope Reactor (HFIR), the world's most powerful steady-state neutron source. This combination provides users with unusually well-rounded, some would say unmatched, materials characterization capabilities.
Neutron Sciences Director Ian Anderson explains that the instruments at these two facilities give scientists complementary views of the structural and dynamic nuances of material samples.
At the High Flux Isotope Reactor the neutron beams are continuous, so the instruments there are excellent for looking at molecular detail inside relatively stable materials. The SNS, on the other hand, produces neutron beams in very intense pulses—60 times a second. These pulses are perfect for looking at things that are changing quickly. The reactor is the bright lamp, while SNS is the stroboscope.
The advantage of having both of these facilities at ORNL is that a researcher can make both kinds of measurements on a range of instruments at a single institution, rather than having to go to multiple facilities to gather comparable data. Anderson cites the example of ongoing studies of a group of complex molecules called dendrimers, or "starburst" polymers. Conventional wisdom was that these dandelion-shaped molecules changed size in response to changes in the electrical charge or acidity of their environment.
"At the High Flux Reactor, we conducted studies to test the assumption that increased electrical charge or acidity would increase the size of the molecule," Anderson says. "In this case we were looking at the low-resolution structure of the material, the size of the entire molecule, not at individual atoms." The point of determining whether the size of these molecules changed was to determine whether they could be applied to tasks such as delivering drugs to specific places in the body. Because the polymer can be made to look benign to other cells, including cancer cells, it could be engineered to be absorbed by them. Then, once inside the cell, the polymer could deliver a pharmaceutical payload, rather like a Trojan horse.
Measurements made at the reactor indicated that, despite changes in the distribution of the atoms in the molecules, the size of the molecules themselves remains more or less the same. Researchers then took the samples across the ORNL campus to the SNS to determine how the molecules moved under the same conditions and exactly how their distribution changed. All these factors will help determine the suitability of these molecules for a range of applications.
Anderson stresses that a researcher coming to ORNL can choose the instrumentation at each facility that is best adapted to making the necessary measurements and then combine the results to get a comprehensive look at the material being studied.
More than one-half of the users in the neutron sciences program currently conduct research at both the SNS and the High Flux Isotope Reactor during their stay at the laboratory, but for some the attraction does not end there. "Some users are particularly attracted to ORNL by the analytical capabilities of the reactor and the SNS combined with the nanoscale engineering capabilities of the Center for Nanophase Materials Sciences," Anderson explains. "So in one project a researcher can synthesize a material at the nanocenter and make multiple measurements of its structural and dynamic characteristics at both the reactor and the SNS without leaving the site."
In fact, visitors to ORNL have access to an unusually broad range of materials characterization capability. "When you include ORNL's SHaRE microscopy facility, the High Temperature Materials Laboratory's materials measurement characterization capabilities and our world-class computing facilities," Anderson says, "one realizes that ORNL has a combination of capabilities that would be hard to match anywhere in the world."
Web site provided by Oak Ridge National Laboratory's Communications and External Relations